What the 'Fric' is it?

[RideRate]

Probably a hydraulic accumulator and/or valving unit for the interconnection of the left and right suspensions. Might even be connected to the front suspension too but its not so clear in that picture.

None of this is new technology. It similar to the old Kinetic (now owned by Tenneco I believe) suspension system. Below you will see two accumulators in such a system. What they are doing would be something similar, but the exact plumbing is impossible to know really.

http://www.caroto.gr/static/media/2011/ ... -bar-3.jpg

I read this far and I'm stopping here. Why? Because this is most likely the system in use. It is most likely not any of the other crazy ideas floating around. We'll know eventually.

This system can be implemented across traditional dampers or not, it doesn't matter. The system as shown only decouples roll but by interconnecting the heave dampers (actuators) you get the same concept in pitch. The accumulators may be interconnected and more complicated so as to give you some tuning of roll rates, pitch rates, and roll moment distribution. That's where the clever part comes in to tune the inherent issues from running this set up.

Note the system ONLY gives accumulator driven stiffness in pure pitch and roll. The heave stiffness and warp stiffness from the system are ZERO. So you still need heave springs, wheel springs, etc. to define those modes, but they can now be decoupled from pitch and roll.

I'd guess heave spring is same as always, tuned to set height at downforce levels. Single wheel rates (and warp rates) are now lower giving enhanced mechanical grip and feel, but there is no compromise in the pitch and roll rates because of this. Those rates are set very high with slight negative feedback control from opposite wheels and thus aerodynamic attitude is overall improved.

Just my quick guess. Simple really.


One extra thing to note. The system will work on traditional dampers, but the pistons need to be solid or very stiffly valved in order to drive fluid to a partnered corner's chamber and not allow much to pass across its own main piston. Basically the damper's normal valving needs to be moved somewhere in the desired fluid path and removed from its traditional location on the piston. This could be done in a manifold that also holds the accumulator circuitry. Think about it.

[RideRate]

....if so, how such switching might be triggered ?

I haven't looked at a moog valve cutaway in many years, but going from memory, how about entering mechanical perdition and replacing the electro-mechanical solenoids that displace the magic finger with some lateral G sliding/rolling/bending weight on an arm gizmo. good luck setting it up and having it work reliably. (i'll have to look up a valve schematic before any of you take this seriously....)

It's been done, but never raced. It's in an old racecar engineering.

However, using a flapper/nozzle servovalve won't work here, because you still need the constant high pressure supply to drive the pilot stage and main spool and since there is no pump involved....

You could directly drive a spool valve, but I think to get the desired effect from the system this type of switching is very unnecessary.

[KeithYoung]

It's been done, but never raced. It's in an old racecar engineering.

Do you know which year and month it was in?

[RideRate]

Keith,
June 2011.

After re-reading this article it is fascinating how the suspension problem to solve has been the exact same for decades. The problem and the desired characteristics are no secret, yet it's taken this long post active control to really make some progress in f1. I guess I'm just surprised in the delay of the use of a known passive solution.

[RideRate]

Let's just put it this way. Hydraulic fluid is by no means a spring, especially for use on a car weighing 640kg. It's merely a mode of transporting forces, and multiplying them. It's not intended to store energy like a spring would.

Apologies, ringo, that is how you would like fluid to behave, but it doesn't (quite), and the difference can be important. A column of fluid can be modelled quite accurately as a spring - stiff, perhaps, but a spring nevertheless.

DaveW,
I hear what you're saying, and you harp hard on fluid compliance (as I finally read most all of this thread and hate myself for doing it), but simply put there is no better solution.

Hydraulic fluid itself is as incompressible as a flexible power transmission system gets. Yes, it can be modeled as a spring (stiff, sure) but everything on the planet can be modeled as a spring.

My argument is that fluid compliance is real and under certain circumstances must be accounted for, but it is as inherently non-compliant as it gets and whatever compliance issues arise can be accounted for (aka model it as a spring and solve the problem). In the end, given proper design, hydraulic system response time will always be adequate to create some kind of positive effect. I'm sure this type of thing is tuned in the controls of your rig and it's not rocket science. Pneumatic systems have a limit where they become junk, but I would argue in the real world fluid power does not. Perfect? No. Adequate? Always.

My experiences with damper fluid compliance are opposite of yours. Any phenomena I've attempted to pass off to fluid compliance has turned out to been anything but. It always turns out there is a better explanation (read as damper fluid proves again to be damn near incompressible and it actually behaves that way). Now, damper fluid when used improperly doesn't exhibit this, but this is not the fluid itself acting compliant.

I have a hard time believing the results of the plots you posted earlier in the thread are attributed to fluid compressibility. I just can't fathom it from my experience. And you yourself admit you haven't proven it, just failed to prove otherwise. There is something else at play there.

Same take on the damper thread with the post you pointed to. Pretty sure that cannot be contributed to fluid compliance.

I still think the FRIC system is most likely hydraulically connected in order to decouple the stiffness of all modes. I also say pitch and roll stiffnesses are set by their respective accumulators. In this case we can probably go right to treating the hydraulic fluid as incompressible and just model all compliance as the gas charge in the accumulator. Taking the next step I'd go to the compliance of the fluid lines themselves and then I'd think the inertance from all the fluid in the lines is much more a factor at play than the fluid compliance. Hydraulic is the solution to this style suspension and compliance should be no problem for which to compensate.

Thanks for all your input into this thread, it was a fun read.

[marcush.]

it might not be the fluid which is compressible ,but the system will show some compliance or hysteresis and no matter how hard you are trying so even the term spring is maybe not correct for the pheneomenons in the system?

[GSpeedR]

Same take on the damper thread with the post you pointed to. Pretty sure that cannot be contributed to fluid compliance.

I have 2 points. As you said, the compliance for hydraulic oil is quite low, but it is not zero. So there will be a non-zero volume change in response to a pressure change. Looking at an entire damper chamber in its entirety, I would say it is probably safe to assume that the cross-sectional area is large enough that there will not be a significant axial deflection. However, at the flow ports at the piston and bleed orifices, this cross-section becomes much smaller and thus a similar pressure change will create more axial displacement. Keep in mind that local pressure gradients near the flow restrictions are much higher than the average pressure changes in the chambers, making this axial compliance more significant.

The second point is that an emulsified fluid is still a fluid. It is probably not possible to completely evacuate air during the assembly of a damper. Even more important is that the high local pressures at the restrictions can create local cavitation of the fluid. The bulk modulus for a cavitated oil is much lower (much higher compliance) than a pure hydraulic oil. This cavitation is often reversed once the oil passes the restrictions. I like to think of the problem as 2 mostly rigid columns of oil representing the chambers with a smaller much more compliant column enclosing the piston/shims. A low-amplitude, high-frequency input can certainly exaggerate this 'hysteretic' effect. Any oil with flow orifices can experience this (including servo-hydraulic equipment), but whether it is significant depends on the pressures involved, and the geometry of the system.

So all that is additive with other forms of compliance: expansion of the shock body or lines, deflection of the piston on the shaft, etc. I still call the overall effect 'fluid compliance' though it may be a bit of a misnomer.

[RideRate]

GSpeedR,
You make very good points and maybe this is all semantics. As a designer of systems for these parts I tend to think of things in terms of the addends and not just in terms of the summation. All said and done, it is only the summation that is important but working on the components is key to the system design. Local cavitation is definitely an issue and something I pay lots of attention to. As for the entrained air, there seems to be a point of how much you can get out and in terms of building a damper it is obvious if that level has or has not been achieved. But it's the cavitation that can wreck your fluid's compressible behavior.

Low amp/higher frequency is without a doubt the distinct phenomenon of concern. How it comes about can be very complex. There are some very important possible shock compliances you don't mention such as mounts (rubber bushings and freeplay in sphericals or bolts/pins) and then there are all the seals/orings/wearbands/etc.

[DaveW]

Note the system ONLY gives accumulator driven stiffness in pure pitch and roll. The heave stiffness and warp stiffness from the system are ZERO. So you still need heave springs, wheel springs, etc. to define those modes, but they can now be decoupled from pitch and roll.

Not quite sure that I follow your argument, RideRate. Consider the heave/pitch case. You state that you require springs to control heave, but the "Fric" system provides pitch springing, which allows the two modes to be decoupled. Surely that will be the case only if you want to increase the pitch spring rate over that provided by the (physical) heave springs.

Putting it simply, I suspect that an aerodynamicist would like very stiff heave springs to control the aero platform, but lower rate pitch springs to allow the vehicle to follow the road. A reduction in the "natural" pitch spring rate can be implemented (as in hydragas), but the system had better be capable of shoveling fluid between the two actuators in a controlled way at around the 9 Hz. necessary to control the pitch mode of an open wheeler. That isn't so easy to achieve.

[DaveW]

Same take on the damper thread with the post you pointed to. Pretty sure that cannot be contributed to fluid compliance.

You don't have to take my word for it, read the second paragraph of this. I think that GSpeedR is correct (on both points).

[RideRate]

Same take on the damper thread with the post you pointed to. Pretty sure that cannot be contributed to fluid compliance.

You don't have to take my word for it, read the second paragraph of this. I think that GSpeedR is correct (on both points).

I know that paper well. I've done lots of detailed work with shock pressures including balancing. I watch more shock pressure traces than any sane human should. I know lots of old Penske guys. Just cause they say it simplified in a quick paper doesn't mean much of anything to me so I don't need Penske's word.

I also think GSppedR is correct on both points. Actually on all 3 points.

[ringo]

I think ultimately, the fluid properties were not the main centre of the FRIC system as some suggested.
The hydraulic oil's spring rate was not intended to provide the support for the car.
You guys may now continue the discussion.

If i may as riderate, could you put in bullet form or in a table, the FRIC properties in terms of the motion of the car; heave roll etc. versus the typical systems used.
I feel that would more solidify what we are aiming to find out in this thread.

[mep]

I have to agree with Ringo. I thought we already managed to agree that fluid compression does exist but is not the main issue of the system. I am a bit surprised this argument flamed up again.

[GSpeedR]

When I first heard that F1 teams were hydraulically interconnecting suspensions, I got excited thinking they were creating a low-warp modal suspension to improve tire variation as well as platform control. However, it does seem that it is purely for aero control, which is less fun for me, but still interesting.

[RideRate]

You state that you require springs to control heave, but the "Fric" system provides pitch springing, which allows the two modes to be decoupled. Surely that will be the case only if you want to increase the pitch spring rate over that provided by the (physical) heave springs.

Yes, exactly.

Putting it simply, I suspect that an aerodynamicist would like very stiff heave springs to control the aero platform, but lower rate pitch springs to allow the vehicle to follow the road.

My guess would've been higher pitch rates for decreased variation in aerodynamic platform would greatly outweigh having low pitch rates to "follow the road".